JP2582562B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

The present invention relates to an air-fuel ratio control device for an internal combustion engine.

<Prior Art> In an internal combustion engine equipped with an electronically controlled fuel injection device, a fuel injection valve is opened by a drive pulse signal given in synchronization with the rotation of the engine. The fuel is to be injected. Therefore, the fuel injection amount is controlled by the pulse width of the drive pulse signal. If the pulse width is set as Ti and a control signal corresponding to the fuel injection amount is obtained, to obtain the stoichiometric air-fuel ratio which is the target air-fuel ratio, Ti is given by the following equation. Determined by

Ti = Tp · COEF · α + Ts where Tp is a basic pulse width corresponding to the basic injection amount, and is referred to as a basic injection amount for convenience. Tp = K · Q / N where K is a constant, Q is the engine intake air flow rate, and N is the engine speed. COEF is various correction coefficients such as water temperature correction. α is a feedback correction coefficient for air-fuel ratio feedback control (λ control) described later. Ts is a voltage correction amount for correcting a change in the injection flow rate of the fuel injection valve due to a change in the battery voltage.

For λ control, an O ₂ sensor is provided in the exhaust system to detect the actual air-fuel ratio, and control is performed by comparing whether the air-fuel ratio is higher or lower than the stoichiometric air-fuel ratio with the slice level, and therefore, The feedback correction coefficient α is determined, and the stoichiometric air-fuel ratio is maintained by changing this α.

Here, the value of the feedback correction coefficient α is changed by proportional integration (PI) control to achieve stable control.

That is, the output voltage of the O ₂ sensor is compared, and when the air-fuel ratio is higher (higher) or lower than the slice level, the air-fuel ratio is not suddenly increased or decreased. First, the air-fuel ratio is controlled so as to decrease (increase) by P and then gradually decrease (increase) by I minutes to decrease (increase) the air-fuel ratio.

However, under the condition that λ control is not performed, α is clamped, and a desired air-fuel ratio is obtained by setting various correction coefficients COEF.

<Problems to be Solved by the Invention> However, in the method of performing the feedback correction coefficient by so-called PI control during the air-fuel ratio feedback control as described above, the control is performed in consideration of only the magnitude relationship between the air-fuel ratio and the stoichiometric air-fuel ratio. As a result, the amount of overshoot and undershoot becomes large, and as a result, the fluctuation range of the air-fuel ratio is too large to generate a large surge torque, thereby deteriorating the ride comfort and the purification efficiency of the exhaust purification catalyst, resulting in poor CO, HC, NO There were problems such as the inability to sufficiently control the amount of emission of _{x and the} like.

The present invention has been made in view of such a conventional problem, and by adopting a configuration in which the feedback correction coefficient is set in consideration of the speed of change of the air-fuel ratio, the fluctuation of the air-fuel ratio is more effectively achieved. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which suppresses, thereby reduces the surge torque and stabilizes engine rotation, and enhances exhaust purification performance.

<Means for Solving the Problems> For this reason, the present invention provides an engine operating state detecting means for detecting an engine operating state as shown in FIG. 1, and a basic fuel supply amount based on the detected engine operating state. Means for setting the basic fuel supply amount to be set; air-fuel ratio detecting means for detecting the air-fuel ratio of the air-fuel mixture to be taken into the engine; comparing the detected air-fuel ratio with the target air-fuel ratio; Feedback correction coefficient setting means for setting a feedback correction coefficient for feedback-correcting the basic fuel supply amount by integral control or proportional integral control; and an air-fuel ratio detection value change rate for calculating a change rate of a detection value by the air-fuel ratio detection means. Calculating means; air-fuel ratio detection value deviation calculating means for calculating a deviation of the detection value from the reference value by the air-fuel ratio detecting means; change speed of the air-fuel ratio detection value and reference value of the air-fuel ratio detection value A feedback correction coefficient correction value setting means for setting a correction value of the feedback correction coefficient so as to correct the feedback correction coefficient set by the feedback correction coefficient setting means, based on the deviation from the basic fuel supply amount setting. Means for setting the fuel supply amount based on the basic fuel supply amount set by the means, the feedback correction coefficient set by the feedback correction coefficient setting means, and the correction value set by the feedback correction coefficient correction value setting means. Means, and fuel supply means for supplying fuel to the engine in accordance with a fuel supply signal corresponding to the fuel supply amount set by the fuel supply amount setting means.

<Operation> The basic fuel supply amount setting means sets the basic fuel supply amount corresponding to the target air-fuel ratio based on the engine operation state detected by the engine operation state detection means.

On the other hand, the air-fuel ratio detected by the air-fuel ratio detecting means is compared with the target air-fuel ratio by the feedback correction coefficient setting means, and the feedback correction coefficient for performing the feedback correction of the basic fuel supply amount according to the magnitude relation between the two is integrated control or Set by proportional integral control.

In parallel with this, the air-fuel ratio detection value change speed calculation means calculates the change speed of the air-fuel ratio detection value by the air-fuel ratio detection means, and the air-fuel ratio detection value deviation calculation means calculates the air-fuel ratio detection value from the reference value of the air-fuel ratio detection value. Is calculated.

Then, the feedback correction coefficient correction value setting means includes:
A correction value of the feedback correction coefficient is set so as to correct the feedback correction coefficient set by the feedback correction coefficient setting means based on the calculated change rate and deviation of the detected air-heat ratio.

The fuel supply amount setting means sets the fuel supply amount based on the basic fuel supply amount, the feedback correction coefficient, and the feedback correction coefficient correction value set by the setting means.

The fuel supply means supplies fuel to the engine according to the fuel supply signal corresponding to the fuel supply amount set as described above.

<Example> Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 2 shows the configuration of an air-fuel ratio control device (electronically controlled fuel injection device) for an internal combustion engine according to the present invention.

In the figure, air is sucked into an internal combustion engine 1 through an air cleaner 2, an intake duct 3, a throttle chamber 4, and an intake manifold 5.

The intake duct 3 is provided with a hot wire flow meter 6 for detecting the intake air flow rate Q, and outputs a voltage signal Us corresponding to the intake air flow rate Q. The throttle chamber 4 is provided with a throttle valve 7 interlocked with an accelerator pedal (not shown), and controls the intake air flow rate Q. Intake manifold 5
Is provided with an electromagnetic fuel injection valve 8 as a fuel supply means for each cylinder. The fuel injection valve 8 is driven to open by an injection pulse signal from a control unit 10 having a microcomputer described later. The fuel supplied from the pressure regulator is controlled to a predetermined pressure by the pressure regulator to inject and supply the fuel into the intake manifold 5. Further, a water temperature sensor 11 for detecting a cooling water temperature Tw in a cooling jacket 14 of the engine is provided, and an air-fuel ratio for detecting an air-fuel ratio in the intake air-fuel mixture by detecting an oxygen concentration in the exhaust gas in the exhaust passage 12. An oxygen sensor 13 is provided as detection means.

The control unit 10 detects the engine speed N by counting a crank unit angle signal output in synchronization with the engine rotation from the crank angle sensor 9 for a fixed time or measuring the cycle of the crank reference angle signal.

The hot wire flowmeter 6, the crank angle sensor 9 and the water temperature sensor 11 constitute an engine operating state detecting means.

The control unit 10 calculates the fuel injection amount Ti based on the various detection signals detected as described above, and controls the driving of the fuel injection valve 8 based on the set fuel injection amount Ti.

Air-fuel ratio control by control unit 10
This will be described with reference to the flowchart shown in FIG. 4 and FIG.

FIG. 3 shows a routine for setting a feedback correction coefficient LAMBDA used for calculating the fuel injection amount and a corrected value of LAMBDA, and this routine is executed for each revolution of the engine.

In step (referred to as S in the figure, the same applies hereinafter) 1, the output voltage S from the oxygen sensor 14 is read.

In step 2, comparing the output voltage S and the reference voltage of the stoichiometric air-fuel ratio corresponding to set the integration error E in accordance with the difference voltage [Delta] S ₁ obtained by subtracting the latter from the former. Specifically, as shown in FIG. 5, when the deviation voltage ΔS ₁ has a positive maximum, E
Minimum positive maximum value PB (e.g. 1), the E where [Delta] S ₁ corresponds to the value of the positive middle-level E where positive intermediate value PM, [Delta] S ₁ corresponds to a positive small value positive Where the value PS, ΔS ₁ corresponds to a value near 0, E is 0, and where ΔS ₁ corresponds to a small negative value, E is the negative minimum value NS, ΔS ₁ corresponds to a negative middle value. At this point, E is set to a negative maximum value NB (for example, -1) where the negative intermediate value NM, ΔS ₁ becomes a negative maximum.

In step 3, the integration error E is compared with 0, and when E> 0, that is, when the air-fuel ratio is rich, the process proceeds to step 4, and it is determined whether or not the first time the air-fuel ratio has changed from lean to rich.

And when it is determined that it is the first time, the process proceeds to step 5,
The feedback correction coefficient LAMBDA by subtracting a predetermined proportional portion P _L from the previous value, the second and subsequent going subtracted by the program proceeds to step 6 a predetermined integral amount _{I L (P L >> I L} ).

When it is determined in step 3 that E <0, that is, when the air-fuel ratio is lean, the process proceeds to step 7 to determine whether or not it is the first time of inversion from rich to lean. the willing LAMBDA to 8 by adding a predetermined proportional amount P _R to the previous value, the second and subsequent continue to incremented by proceeds to step 9 a predetermined integral amount _{I R (P R >> I R} ).

When it is determined in step 3 that E = 0, LAMBDA is not increased or decreased and is kept at the previous value.

The functions of steps 1 to 9 for setting the feedback correction coefficient LAMBDA constitute feedback correction coefficient setting means.

Next, in steps 10 to 12, a correction value PID for correcting the feedback correction coefficient LAMBDA is set.

First, at step 10, the deviation voltage Δ obtained by subtracting the previous output voltage from the current output voltage of the oxygen sensor 14
Setting the proportional error ΔE according to S _2.

Maximum value PB range proportional error E positive in this case sixth positive maximum value - the maximum negative value of the deviation voltage [Delta] S ₂ as shown in FIG similarly to the case of setting the integration error E is also positive Intermediate value PM, positive minimum value PS, 0, negative minimum value NS, negative intermediate value NM, negative maximum value N
Set to 7 stages of B.

The proportional error ΔE in this case is set as a value corresponding to the changing speed of the output voltage (air-fuel ratio detection value) of the oxygen sensor 14.

Therefore, the function of step 10 constitutes the air-fuel ratio detected value change speed detecting means.

Next, in step 11, when setting a correction value of the feedback correction coefficient LAMBDA for the value ΔE corresponding to the air-fuel ratio detection value change speed, so-called fuzzy inference is applied,
The fuzzy amount U in that case is calculated.

The fuzzy inference (control) is, in short, for example, taking into account the certainty (fuzzy amount) of a proposition such as making the operation amount (control amount) positive or negative with respect to the input amount (detection value),
The operation amount is set by weighting the fuzzy amount.

As a method of setting the fuzzy amount, there is a complicated method such as setting each fuzzy amount for the first-order difference or the second-order difference of the control deviation and collectively obtaining the fuzzy amounts from each fuzzy amount. As a simple method, a fuzzy amount U is set as shown in FIG. 7 by weighting the proportional error ΔE in consideration of the integral error E.

That is, when ΔE corresponding to the change speed of the air-fuel ratio detection value is a large positive value, that is, when the change in the air-fuel ratio in the rich direction is large, excessive enrichment of the air-fuel ratio due to overshoot is suppressed. Therefore, the correction control amount for correcting the air-fuel ratio in the lean direction should be increased. However, also Δ
Even if E is a large positive value, when the integration error E corresponding to the detected value of the air-fuel ratio is a large negative value, that is, when the air-fuel ratio is lean, the feedback correction coefficient becomes a large value in the rich direction. Since it is set, it is preferable to increase the correction control amount in the lean direction and control the enrichment due to overshoot earlier, but when E is a positive large value, that is, when the air-fuel ratio is rich Since the feedback correction coefficient is set to a large value in the lean direction, if the correction control amount in the lean direction based on ΔE is too large, the leaning is excessively advanced due to undershoot, so that it should not be too large.

Accordingly, the absolute value of the fuzzy amount U is adjusted so that the positive value corresponds to the correction control in the rich direction (the feedback correction coefficient LAMBDA is increased and corrected) and the negative value is the correction control in the lean direction (the LAMBDA is reduced and corrected). When the value of .DELTA.E is a positive value and the value of E is a negative value, the fuzzy amount U is increased by a negative value. The larger the negative value and the larger the value of E is a positive value, the larger the fuzzy amount U is a positive value. In the case of the fuzzy amount U, similarly to the case of E and ΔE, the positive maximum value
Seven levels are set from (for example, 1) to the maximum negative value NB (for example, -1).

In step 12, the correction value of the feedback correction coefficient LAMBDA is adjusted according to the fuzzy amount U set as described above.
Calculate the PID.

This is because, as shown in FIG. 8, the larger the fuzzy amount U is a positive value, the larger the LAMBDA increase correction amount is.
The correction value PID multiplied by MBDA is increased (for example, maximum value = 1.05), and when U = 0, no correction is performed so that PID is not performed.
= 1 and the correction value PID is made smaller as the fuzzy amount is a negative value and larger (for example, the minimum value = 0.95).

The functions of steps 10 to 12 constitute the feedback correction coefficient correction value setting means.

Next, the feedback correction coefficient obtained as described above
A routine for calculating the fuel injection amount Ti using the LAMBDA and its correction value PID will be described with reference to the flowchart shown in FIG.

This routine is executed at regular intervals (for example, every 10 ms).

In step 21, the intake air flow rate Q detected by the hot wire flowmeter 6 and the engine speed N detected based on a signal from the crank angle sensor 9 are input.

In step 22, based on the intake air flow rate Q and the engine speed N, a basic fuel injection amount Tp proportional to the intake air amount per unit rotation of the engine is calculated by the following equation.

Tp = K · Q / N (K is a constant) The functions of these steps 21 and 22 constitute basic fuel supply amount setting means.

In step 23, various correction coefficients COEF according to the cooling water temperature Tw detected by the water temperature sensor 11 and the like are set.

In step 24, the voltage correction Ts is set based on the battery voltage value.

In step 25, it is determined whether or not the condition is the λ control condition.

Here, if the condition is not the λ control condition, for example, in a high rotation / high load region, the process proceeds to step 26, and the process proceeds to step 28 described below in a state where the feedback correction coefficient LAMBDA and the correction value PID are clamped to the previous values (or reference values). move on.

In the case of the λ control condition, the routine proceeds to step 27, where the feedback correction coefficient LAMBDA and the correction value PID set in the routine shown in FIG. 3 are input.

In step 28, the fuel injection amount Ti is calculated according to the following equation.

Ti = Tp · COEF · LAMBDA · PID + Ts The function of step 28 constitutes a fuel supply amount setting means.

When the fuel injection amount Ti is calculated in this way, the Ti
Is applied to the fuel injection valve 8 at a predetermined timing in synchronization with the rotation of the engine, and fuel injection is performed.

In the fuel injection control according to the present invention described above, the feedback correction coefficient LAMBDA is corrected by predicting the change state of the air-fuel ratio by the correction value PID set based on the change speed of the air-fuel ratio detection value. In addition, the fluctuation of the air-fuel ratio due to the feedback control can be effectively suppressed.
Particularly in the case of this embodiment, as shown in FIG. 9, the correction value PID can be set to a more appropriate value by using fuzzy inference, so that the air-fuel ratio can be stabilized as much as possible, and the surge torque can be reduced. As a result, the riding comfort can be improved and the exhaust purification performance can be enhanced.

<Effects of the Invention> As described above, according to the present invention, the feedback control amount is corrected while sequentially predicting the change state of the air-fuel ratio based on the change speed of the detected air-fuel ratio value and the deviation from the reference value. Because of the configuration, the fluctuation of the air-fuel ratio can be suppressed as much as possible, thereby improving the riding comfort and the exhaust purification performance by reducing the surge torque as much as possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, and FIG.
Flow chart showing MBDA and PID calculation routine, fourth
FIG. 5 is a flowchart showing a fuel injection amount calculation routine of the embodiment, FIG. 5 is a map for setting an integral error E used in the embodiment, and FIG. 6 is a proportional error ΔE used in the embodiment.
FIG. 7 is a map for setting a fuzzy amount U used in the above embodiment, FIG. 8 is a map for setting a correction value PID used in the above embodiment, and FIG. It is a time chart which shows various state quantities. 1 ... engine, 6 ... hot wire flow meter, 8 ... fuel injection valve, 9
…… Crank angle sensor, 10 …… Control unit,
11 ... Water temperature sensor, 13 ... Oxygen sensor

Claims (1)

(57) [Claims] 1. An engine operating state detecting means for detecting an engine operating state; a basic supply amount setting means for setting a basic supply amount of fuel based on the detected engine operating state; Air-fuel ratio detecting means for detecting the air-fuel ratio, comparing the detected air-fuel ratio with the target air-fuel ratio, and integrating or controlling a feedback correction coefficient for feedback-correcting the basic fuel supply amount according to the magnitude relationship between the two. Feedback correction coefficient setting means set by proportional integration control; air-fuel ratio detection value change speed calculation means for calculating the change speed of the detection value by the air-fuel ratio detection means; and deviation of the detection value from the reference value by the air-fuel ratio detection means from the reference value. An air-fuel ratio detection value deviation calculating means for calculating; and a feedback correction coefficient setting means based on a change speed of the air-fuel ratio detection value and a deviation of the air-fuel ratio detection value from a reference value. Feedback correction coefficient correction value setting means for setting a correction value of the feedback correction coefficient so as to correct the feedback correction coefficient set by the control means; a basic fuel supply amount set by the basic fuel supply amount setting means; Fuel supply amount setting means for setting the fuel supply amount based on the feedback correction coefficient set by the means and the correction value set by the feedback correction coefficient correction value setting means. Air-fuel ratio control device.